Vehicle manufacturers are required to install on-board diagnostic (e.g., OBD-II) systems on light-duty automobiles and trucks. On-board diagnostic systems monitor a vehicle's electrical and mechanical systems and generate data that can be processed by a vehicle's engine control unit (ECU) to detect any malfunction or deterioration in the vehicle's performance. Most ECUs transmit status and diagnostic information over a shared, standardized electronic bus in the vehicle. The bus effectively functions as an on-board computer network, with many processors transmitting and receiving data via the bus. Data available from the ECU may include vehicle speed, fuel level, engine temperature, intake manifold pressure, etc.